This invention relates generally to a resist ink to be used in the fabrication of printed circuit boards and, more particularly, to a resist ink composition suitable for forming on a board a printed, masking pattern which is resistive against chemical plating.
One such a resist ink is a two-part ink composed of a first part containing an epoxy resin, a filler, such as silica or aluminum silicate, and an organic solvent and a second part containing a curing agent, a curing-accelerating catalyst and an organic solvent. In use, the two parts are mixed with each other and the mixture is printed on an insulated board by screen printing. The board with the resultant resist masking pattern is then subjected to a chemical plating treatment for the formation of the desired copper wiring pattern on the board.
The known resist ink has the following problems. Firstly, the physical properties such as viscosity and thixotropy of the ink tend to change with time so that it is difficult to obtain stable printed patterns. Secondly, in repeated screen printing with the ink on boards, fine partterns are failed to be reproduced well. That is, with the known ink, it is difficult to form, with satisfactory reproducibility, fine patters with a line width of, for example, about 200 .mu.m. Thirdly, the resistance of the masking pattern against chemical attach by a chemical plating liquor is not fully satisfactory so that it cannot withstand severe conditions required in a high speed plating process. The fourth problem is directed to the deposition of Cu on the resist masking pattern. Growth of such deposits will cause short circuit of the wiring pattern.